Santhosh hails is from
Thiruvananthapuram, India. He is the only son of retired headmaster C. N. Kesavan Nair and P. Rajalakshmiamma, who is also a retired teacher. He grew up along with his two sisters in
Pettah, Thiruvananthapuram. Santhosh was brought up by his maternal grandparents, advocate K. S. Chellappan Pillai and B. Parukuttyamma, ever since his parents left to
Ethiopia on deputation. He did his schooling at
St. Joseph's Higher Secondary School, Thiruvananthapuram. Both his sisters turned out to be gynaecologists while he wanted to pursue a career as an actor. He graduated and post graduated in mathematics from
Mahatma Gandhi College, Thiruvananthapuram. He was active in politics during his college days. ==Film career==